Generally, the lithographic press prints in such a way that a printing plate is wound on a plate cylinder while being mechanically fastened thereonto. A lithographic printing plate uses a support of a material other than metal (e.g., plastic film, paper or the like), which is easy to handle. However, it is not satisfactory in its dimensional stability. For example, friction between a blanket cylinder and a form plate causes a partial strain resulting in the deformation of the form plate, thereby degrading the printing dimensions and the accuracy of the printing positions relative to a printing paper.
The form plate using a support made of such a material has been used in a limited type of printing, e.g., a simple printing for a small number of prints, which does not require a high registration accuracy. Some modification or alteration needs to be made on the form plate when it is used for standard printing, e.g., high grade printing of multi-color, large scale printing machines or the like.
To cope with this problem, the Japanese Utility Model Unexamined Publication No. Sho. 58-1046 suggested that a plate material should be directly bonded to a preparatory form plate or form cylinder by use of a double-coated adhesive sheet or by use of a spray adhesive of acrylic or rubber material.
This method firmly bonds the printing plate to the plate cylinder. The firm bonding by this method does not allow fine position adjustment of the printing plate on the plate cylinder, and makes it extremely difficult to remove the form plate after printing.
A plate-forming and printing method based on a CTP (computer to plate), which gradually increases its presence in the market, is superior to the conventional plate-forming and printing method (whose exposure step/process for the plate material is based on a close-contact exposure using a lith film), in that the size and position accuracy of an image (exposure) to the plate material is good, and the registration is easy in multi-color printing. However, the lithographic printing plate using the support of a plastic film, a paper or the like, fails to fully utilize the advantage of easy registration in multi-color printing by the CTP because of its disadvantage referred to above.